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Resolution of racemic aminoalcohols (β-blockers), amines and acids as enantiomeric derivatives using a chiral α1-acid glycoprotein column
Jonriwl of Chromatography, 325 (1985) 319-384 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands CHROM. 17 612
RESOLUTION OF RACEMIC AMINOALCOHOLS (B-BLOCKERS), AMINES AND ACIDS AS ENANTIOMERIC DERIVATIVES USING A CHIRAL al-ACID GLYCOPROTEIN COLUMN
Jc)RGEN HERMANSSON Apoteksbolaget AB, Central Laboratory. Box 3045, S-171 03 Solna (Swede) (Received January 29th, 1985) I
SUMMARY
A 3-cm long al-acid glycoprotein column (commercially available as EnantioPat) has been used for the enantiomeric resolution of fl-blockers (propranolol, alprenolol, metoprolol, oxprenolol, pindolol). The method is based on the formation of simple enantiomeric derivatives using a solution of phosgene in toluene. A separation factor of 5.7 was obtained for the enantiomers of propranolol. The separation of the mandelic acid methyl and ethyl esters as well as an acetyl derivative of a primary amine is also demonstrated. INTRODUCTION
The al-acid glycoprotein column (al-AGP column) has been used for the resolution of many racemic drt~g&~. Furthermore, the column has also been used in bioanalysis for the separation and quantitation of the enantiomers of disopyramide present in human plasma3. Although the al-AGP column is a powerful tool for the direct resolution of chiral molecules from different compound classes, such as different amines1*2, nonproteolytic compounds and acids4, not all compounds are resolved with high separation factors. Preparation of simple enantiomeric derivatives is one way of increasing the resolution of compounds giving low separation factors, or no resolution at all, in underivatized form. The alternative approach to direct resolution of chiral molecules is the use of diastereomeric derivatives. However, this indirect tecl,mque must be carefully controlled to avoid errors caused by different reaction rates of the enantiomers with the chiral reagent, or by ra cemization during depiatization. It has been demonstrated that the enantiomers of ketamine react at different rates with the chiral reagents, N-tritluoroacetyl- (S)-prolyl chloride and (S.S)-N-trifluoroacetyl proline anhydrides. However, these problems can be avoided by preparation of enantiomeric derivatives, using a non-chiral reagent, followed by chromatography on a chiral column. The present study reports the direct separation, on a 3-cm long alAGP column, of the enantiomeric 2-oxazolidone derivatives of /I-receptor blocking agents. The separation of esters and an acetyl derivative of a primary amine is also reported. 0021-9673/85/$03.30
0
1985 Elsevier Science Publishers B.V.
J. HERMANSSON
380 EXPERIMENTAL
Apparatus The liquid chromatographic system consisted of a Waters Model 6000 A pump, a Waters U6K injector and a Shimadzu SPD-2A variable-wavelengh W detector operated at 215 nm. An ctl-AGP silica column (30 x 3.0 mm I.D. or 100 x 3.0 mm I.D., containing 147 mg of al-AGP per gram of solid phase) with a mean particle diameter of 10 m was usedz. This column is now available as EnantioPace from LKB Produkter AB (Bromma, Sweden). Chemicals Racemic alprenol hydrochloride, metoprolol tartrate, oxprenolol hydrochloride, propranolol hydrochloride, practolol and pindolol were obtained from drug manufacturers. Mandelic acid methyl ester, mandelic acid ethyl ester and mandelic acid were purchased from Sigma (St. Louis, MO, U.S.A.). Trans AJ 1266 was kindly supplied by Professor J. L. G. Nilsson (Apoteksbolaget AB, Central Laboratory, Solna, Sweden). The chemical structures are shown in Figs. 1 and 2. Analytical grade 2-propranol was obtained from E. Merck (Darmstadt, F.R.G.). Phosgene (20% in toluene) was purchased from Fluka (Buchs, Switzerland).
R-O-CH2-~H-~H2-NH-CHKH3)2 OH -
+COC12-
R-0-CH2-;H-\H2 ‘NCH(CH312
O\/ ii
Q /
-
’
R
H t-COOR
Alprenolol
bH
B Mandelic acid
H
Mandelic acid methyl ester
CH3
Oxprenolol
C2HS
Trans AJ 126
NH2 C”3
Fig. 1. Chemical structures. Fig. 2. Reaction of &receptor blocking agents with phosgene.
CH2-CH=CH2
/\ Q
0-CH2-CH=CH2
fletopmlol Mandelic acid ethyl ester
/\
Q-
Pindolol
Propranolol
.
’
ENANTIOMERIC
RESOLUTION OF B-BLOCKERS
381
Preparation of oxazolidone of j&receptor blocking agents Racemic oxazolidone derivatives of the @eceptor blocking agents were formed by reaction with phosgene 7.8. About 1 mg of the “B-blocker” was added to a screw-cap conical test-tube. The substance was dissolved in 0.5 ml of diethyl ether and 0.05 ml of 0.5 M sodium hydroxide, and the mixture was shaken for 1 min before the addition of 50 ~1 of phosgene solution. The mixture was agitated at room temperature in a rotating extraction apparatus. After 1 h of reaction time the tubewas centrifuged at 500 g, and the organic phase was transferred to a new tube and evap orated to dryness. The residue was dissolved in the mobile phase. A reaction scheme is shown in Fig. 2. Acetylation of trans AJ 126 Trans AJ 126 hydrochloride (1 mg) was treated with base and extracted into diethyl ether. The diethyl ether layer was transferred to a new tube and evaporated to dryness under nitrogen. The residue was dissolved in 200 fi of methylene chloride and 50 ,~l of triethylamine. Acetic acid anhydride (250 pl) was added, and after 15 min of reaction time at WC the solution was evaporated to dryness under a stream of nitrogen. The residue was dissolved in the mobile phase, RESULTS AND DISCUSSION
Many racer& drugs have been resolved using an q-acid glycoprotein column (aI-AGP column)1-3. However, it is impossible to design a chiral phase that resolves all classes of compounds with high separation factors. Therefore, it is interesting to investigate the possibilities of increasing the separation factors, of compounds giving low enantioselectivity, by the preparation of simple enantiomeric derivatives. R
(A)
(8)
S
A
_
Ii
min 20 10 0 min 20 0 Fig. 3. Separation of the enantiomers of propanolol and pindolol as oxazolidones. Column, 30 x 3.0 mm I.D.), 147 mg of a,-AGP per gram of solid phase. Mobile phase, (A) 15% (v/v) 2-propanol in phosphate buffer (pH 7.0; p = 0.02), (B) as in A but 4% 2-propanol; flow-rate, 0.5 ml/min.
382
J. HERMANSSGN
TABLE I CHROMATGGRAPHIC
DATA FOR OXAZOLIDGNES
OF /?-BLOCKERS
Conditions: column, 30 x 3.0 mm I.D., 147 mg of al-AGP per gram of solid phase, mobile phase, phosphate buffer @H 7.0; p = 0.02) with the addition of 10% 2-propanol.
Alprenolol Gxprenolol Metoprolol Pindolol Propranolol l
k’,*
a
8.98 28.3 0.40 4.64 26.8
1.57 1.64 1.00 1.65 5.71
Capacity factor of the first eluted enantiomer.
Separation of non-proteolytic enantiomeric derivatives Phosgene derivatives. Recently, Wainer et al.’ reported the resolution of the enantiomers of the aminoalcohol norephedrine as its 2-oxazolidone derivative. They also demonstrated that oxaxolidone formation proceeds without racemization. The enantiomers of #I-receptor blocking agents have also been separated as oxazolidones by gas chromatography*. Wainer et al. resolved the enantiomers of propranolol as the 2-oxazolidone derivatives on a chiral HPLC cohmmg. They obtained a separation factor of 1.09. The present study reports the separation of the enantiomers of /I-receptor blocking agents as the enantiomeric 2-oxazolidone derivatives, using a 30-mm long aI-AGP column and a mixture of phosphate buffer (pH 7; p = 0.02) and 2-propanol as the mobile phase. Typical chromatograms are shown in Fig. 3A and B, where the enantiomers of propranolol and pindolol are separated. (R)-Propranolol is eluted with a lower capacity factor than the @)-form, therefore it is reasonable to assume that this is valid for the other /I-blockers tested. However, a reversal of the elution
I
.,_aii minl0
0 min20 10 0 Fig. 4. Resolution of metoprolol enantiomers as oxazolidones. Column as in Fig. 3; mobile phase, phosphate buffer (pH 7.0; p = 0.02); flow-rate, 0.5 ml/min.
Fig. 5. Separation of the enantiomers of acctylatcd trans AJ 126. Column, 100 x 3.0 mm I.D., 147 mg of a,-AGP per gram of solid phase; mobile phase, 10% (v/v) Zpropanol in phosphate bulk (PH 7.0; p = 0.02); flow-rate, 0.5 ml/min.
.* ENANTIOMERIC RESOLUTION OF b-BLOCKERS
383
order of enantiomers has been observed in a series of closely related compoundslo. Table I summarizes the chromatographic data obtained using 10% (v/v) Zpropanol in phosphate buffer (pH 7.0) as the mobile phase. The chiral carbon of the j&receptor blocking agents is located in the propanolamine side-chain, which is the same in all the compounds studied. This means that these parts of the molecules are also identical after the formation of oxazolidones, and it is only the aromatic parts of the molecules that differ. From the data presented in Table I it can be seen that the aromatic part of the structure has a marked influence on the separation factor and the retention. Propranolol, with an unsubstituted naphthalene ring, gives a separation factor of 5.71, whereas metoprolol, with a p-methoxyethyl-substituted benzene ring as the aromatic part, gives no resolution of the enantiomers and very low retention. However, a decrease of the 2-propanol concentration in the mobile phase markedly increases both the retention and the separation factor. A separation factor of 1.95 was obtained for the metoprolol enantiomers with a mobile phase of phosphate buffer (pH 7.0) with no addition of alcohol (Fig. 4). Alprenolol and oxprenolol, which contain a benzene ring substituted in the o&o-position, give separation factors of the same magnitude (Table I). However oxprenolol, which is more hydrophilic than alprenolol, gives capacity factors that are more than three times higher on the al-AGP column. The opposite retention order was obtained using a normal reversed-phase column (LiChrosorb RP-8)“. A reasonable explanation of the higher retention of oxprenolol on the al-AGP column may be that the oxygen in the allyloxy group interacts specifically with the chiral phase. Ester and acetyl derivatives. Preparation of ester derivatives of acids and acetyl derivatives of amines can be an effective way of increasing the separation factors of acids and amines, respectively. This can be illustrated by the following examples: the enantiomers of mandelic acid have been separated as ester derivatives, and the enantiomers of trans AJ 126, a primary amine (structure see Fig. l), have been separated after acetylation. The resolution of the acetylated trans AJ 126 enantiomers is shown in Fig. 5; a separation factor of 4.95 was obtained, and the peaks had capacity factors of 0.88 and 4.33. The mandelic acid enantiomers were not resolved on an al-AGP column. However, the enantiomers can be separated as methyl and ethyl esters. The chromatographic data are summarized in Table II, and a chromatogram of the separation of TABLE II CHROMATOGRAPHIC DATA FOR MANDELIC ACID AND ITS ESTERS Conditions: column, 100 x 3.0 mm I.D., 147 mg of ai-AGP per gram of solid phase; mobile phase, phosphate buffer (pH 7.0; p = 0.02) with the addition of 2% 2-propanol.
Mandelic acid Mandelic acid methyl ester Mandelic acid ethyl ester l
k’,”
a
1.13
1.00
1.04
1.27
1.47
1.93
Capacity factor of the 6rst eluted enantiomer.
I
J. HERMANSSON
-
mm 5 0 Fig. 6. Resolution of racemic mandelic acid ethyl ester. Column, as in Fig. 5; mobile phase, 2% (v/v) 2propanol in phosphate buffer @H 7.0; p = 0.02); flow-rate, 0.5 ml/mm.
the enantiomers of the ethyl ester derivative is shown in Fig. 6. Acids with pK, values between 3 and 8.5 have also been separated directly on the al-AGP column, without derivatization, with separation factors up to 5. The results will be published elsewhere4. ACKNOWLEDGEMENT
I am grateful to Mr. Christer Bergh for skillful technical assistance. REFERENCES 1 2 3 4 5 6 7 8 9 10 11
J. Hermansson, J. Chromurogr., 269 (1983) 71. J. Hermansson, J. Chromufogr., 298 (1984) 67. J. Hermansson, M. Eriksson and 0. Nyquist, J. Chromarogr., 336 (1984) 321. J. Hermansson and M. Eriksson, J. Liq. Chromatogr., (1985) in press. J. D. Adams, Jr., T. F. Woolf, A. J. Trevor, L. R. Williams and N. castagnoli, Jr., J. Phurm. Sci., 71 (1982) 658. U. Hacksell, A. M. Johansson, L. E. Arvidsson, J. L. G. Nilsson, S. Hjorth, A. Carlsson, H. Wilstrom, D. Sanches and P. Lindberg, J. Med. Chem., 27 (1984) 1003. I. W. Wainer, T. D. Doyle, Z. Hamidzadeh and M. Aldrige, J. Chromutogr., 268 (1983) 107. W. A. Kiinig, K. Ernst and J. Vessman, J. Chromatogr., 294 (1984) 423. I. W. Wainer, T. D. Doyle, K. H. Donn and J. R. Powell, J. Chromurogr., 306 (1984) 405. T. D. Doyle and I. W. Wainer, J. High Resold Chromarogr. Chromatogr. Commun., 7 (1984) 38. S. 0. Jansson, I. Andersson and B. A. Person, J. Chromutogr., 203 (1981) 93.
RESOLUTION OF RACEMIC AMINOALCOHOLS (B-BLOCKERS), AMINES AND ACIDS AS ENANTIOMERIC DERIVATIVES USING A CHIRAL al-ACID GLYCOPROTEIN COLUMN
Jc)RGEN HERMANSSON Apoteksbolaget AB, Central Laboratory. Box 3045, S-171 03 Solna (Swede) (Received January 29th, 1985) I
SUMMARY
A 3-cm long al-acid glycoprotein column (commercially available as EnantioPat) has been used for the enantiomeric resolution of fl-blockers (propranolol, alprenolol, metoprolol, oxprenolol, pindolol). The method is based on the formation of simple enantiomeric derivatives using a solution of phosgene in toluene. A separation factor of 5.7 was obtained for the enantiomers of propranolol. The separation of the mandelic acid methyl and ethyl esters as well as an acetyl derivative of a primary amine is also demonstrated. INTRODUCTION
The al-acid glycoprotein column (al-AGP column) has been used for the resolution of many racemic drt~g&~. Furthermore, the column has also been used in bioanalysis for the separation and quantitation of the enantiomers of disopyramide present in human plasma3. Although the al-AGP column is a powerful tool for the direct resolution of chiral molecules from different compound classes, such as different amines1*2, nonproteolytic compounds and acids4, not all compounds are resolved with high separation factors. Preparation of simple enantiomeric derivatives is one way of increasing the resolution of compounds giving low separation factors, or no resolution at all, in underivatized form. The alternative approach to direct resolution of chiral molecules is the use of diastereomeric derivatives. However, this indirect tecl,mque must be carefully controlled to avoid errors caused by different reaction rates of the enantiomers with the chiral reagent, or by ra cemization during depiatization. It has been demonstrated that the enantiomers of ketamine react at different rates with the chiral reagents, N-tritluoroacetyl- (S)-prolyl chloride and (S.S)-N-trifluoroacetyl proline anhydrides. However, these problems can be avoided by preparation of enantiomeric derivatives, using a non-chiral reagent, followed by chromatography on a chiral column. The present study reports the direct separation, on a 3-cm long alAGP column, of the enantiomeric 2-oxazolidone derivatives of /I-receptor blocking agents. The separation of esters and an acetyl derivative of a primary amine is also reported. 0021-9673/85/$03.30
0
1985 Elsevier Science Publishers B.V.
J. HERMANSSON
380 EXPERIMENTAL
Apparatus The liquid chromatographic system consisted of a Waters Model 6000 A pump, a Waters U6K injector and a Shimadzu SPD-2A variable-wavelengh W detector operated at 215 nm. An ctl-AGP silica column (30 x 3.0 mm I.D. or 100 x 3.0 mm I.D., containing 147 mg of al-AGP per gram of solid phase) with a mean particle diameter of 10 m was usedz. This column is now available as EnantioPace from LKB Produkter AB (Bromma, Sweden). Chemicals Racemic alprenol hydrochloride, metoprolol tartrate, oxprenolol hydrochloride, propranolol hydrochloride, practolol and pindolol were obtained from drug manufacturers. Mandelic acid methyl ester, mandelic acid ethyl ester and mandelic acid were purchased from Sigma (St. Louis, MO, U.S.A.). Trans AJ 1266 was kindly supplied by Professor J. L. G. Nilsson (Apoteksbolaget AB, Central Laboratory, Solna, Sweden). The chemical structures are shown in Figs. 1 and 2. Analytical grade 2-propranol was obtained from E. Merck (Darmstadt, F.R.G.). Phosgene (20% in toluene) was purchased from Fluka (Buchs, Switzerland).
R-O-CH2-~H-~H2-NH-CHKH3)2 OH -
+COC12-
R-0-CH2-;H-\H2 ‘NCH(CH312
O\/ ii
Q /
-
’
R
H t-COOR
Alprenolol
bH
B Mandelic acid
H
Mandelic acid methyl ester
CH3
Oxprenolol
C2HS
Trans AJ 126
NH2 C”3
Fig. 1. Chemical structures. Fig. 2. Reaction of &receptor blocking agents with phosgene.
CH2-CH=CH2
/\ Q
0-CH2-CH=CH2
fletopmlol Mandelic acid ethyl ester
/\
Q-
Pindolol
Propranolol
.
’
ENANTIOMERIC
RESOLUTION OF B-BLOCKERS
381
Preparation of oxazolidone of j&receptor blocking agents Racemic oxazolidone derivatives of the @eceptor blocking agents were formed by reaction with phosgene 7.8. About 1 mg of the “B-blocker” was added to a screw-cap conical test-tube. The substance was dissolved in 0.5 ml of diethyl ether and 0.05 ml of 0.5 M sodium hydroxide, and the mixture was shaken for 1 min before the addition of 50 ~1 of phosgene solution. The mixture was agitated at room temperature in a rotating extraction apparatus. After 1 h of reaction time the tubewas centrifuged at 500 g, and the organic phase was transferred to a new tube and evap orated to dryness. The residue was dissolved in the mobile phase. A reaction scheme is shown in Fig. 2. Acetylation of trans AJ 126 Trans AJ 126 hydrochloride (1 mg) was treated with base and extracted into diethyl ether. The diethyl ether layer was transferred to a new tube and evaporated to dryness under nitrogen. The residue was dissolved in 200 fi of methylene chloride and 50 ,~l of triethylamine. Acetic acid anhydride (250 pl) was added, and after 15 min of reaction time at WC the solution was evaporated to dryness under a stream of nitrogen. The residue was dissolved in the mobile phase, RESULTS AND DISCUSSION
Many racer& drugs have been resolved using an q-acid glycoprotein column (aI-AGP column)1-3. However, it is impossible to design a chiral phase that resolves all classes of compounds with high separation factors. Therefore, it is interesting to investigate the possibilities of increasing the separation factors, of compounds giving low enantioselectivity, by the preparation of simple enantiomeric derivatives. R
(A)
(8)
S
A
_
Ii
min 20 10 0 min 20 0 Fig. 3. Separation of the enantiomers of propanolol and pindolol as oxazolidones. Column, 30 x 3.0 mm I.D.), 147 mg of a,-AGP per gram of solid phase. Mobile phase, (A) 15% (v/v) 2-propanol in phosphate buffer (pH 7.0; p = 0.02), (B) as in A but 4% 2-propanol; flow-rate, 0.5 ml/min.
382
J. HERMANSSGN
TABLE I CHROMATGGRAPHIC
DATA FOR OXAZOLIDGNES
OF /?-BLOCKERS
Conditions: column, 30 x 3.0 mm I.D., 147 mg of al-AGP per gram of solid phase, mobile phase, phosphate buffer @H 7.0; p = 0.02) with the addition of 10% 2-propanol.
Alprenolol Gxprenolol Metoprolol Pindolol Propranolol l
k’,*
a
8.98 28.3 0.40 4.64 26.8
1.57 1.64 1.00 1.65 5.71
Capacity factor of the first eluted enantiomer.
Separation of non-proteolytic enantiomeric derivatives Phosgene derivatives. Recently, Wainer et al.’ reported the resolution of the enantiomers of the aminoalcohol norephedrine as its 2-oxazolidone derivative. They also demonstrated that oxaxolidone formation proceeds without racemization. The enantiomers of #I-receptor blocking agents have also been separated as oxazolidones by gas chromatography*. Wainer et al. resolved the enantiomers of propranolol as the 2-oxazolidone derivatives on a chiral HPLC cohmmg. They obtained a separation factor of 1.09. The present study reports the separation of the enantiomers of /I-receptor blocking agents as the enantiomeric 2-oxazolidone derivatives, using a 30-mm long aI-AGP column and a mixture of phosphate buffer (pH 7; p = 0.02) and 2-propanol as the mobile phase. Typical chromatograms are shown in Fig. 3A and B, where the enantiomers of propranolol and pindolol are separated. (R)-Propranolol is eluted with a lower capacity factor than the @)-form, therefore it is reasonable to assume that this is valid for the other /I-blockers tested. However, a reversal of the elution
I
.,_aii minl0
0 min20 10 0 Fig. 4. Resolution of metoprolol enantiomers as oxazolidones. Column as in Fig. 3; mobile phase, phosphate buffer (pH 7.0; p = 0.02); flow-rate, 0.5 ml/min.
Fig. 5. Separation of the enantiomers of acctylatcd trans AJ 126. Column, 100 x 3.0 mm I.D., 147 mg of a,-AGP per gram of solid phase; mobile phase, 10% (v/v) Zpropanol in phosphate bulk (PH 7.0; p = 0.02); flow-rate, 0.5 ml/min.
.* ENANTIOMERIC RESOLUTION OF b-BLOCKERS
383
order of enantiomers has been observed in a series of closely related compoundslo. Table I summarizes the chromatographic data obtained using 10% (v/v) Zpropanol in phosphate buffer (pH 7.0) as the mobile phase. The chiral carbon of the j&receptor blocking agents is located in the propanolamine side-chain, which is the same in all the compounds studied. This means that these parts of the molecules are also identical after the formation of oxazolidones, and it is only the aromatic parts of the molecules that differ. From the data presented in Table I it can be seen that the aromatic part of the structure has a marked influence on the separation factor and the retention. Propranolol, with an unsubstituted naphthalene ring, gives a separation factor of 5.71, whereas metoprolol, with a p-methoxyethyl-substituted benzene ring as the aromatic part, gives no resolution of the enantiomers and very low retention. However, a decrease of the 2-propanol concentration in the mobile phase markedly increases both the retention and the separation factor. A separation factor of 1.95 was obtained for the metoprolol enantiomers with a mobile phase of phosphate buffer (pH 7.0) with no addition of alcohol (Fig. 4). Alprenolol and oxprenolol, which contain a benzene ring substituted in the o&o-position, give separation factors of the same magnitude (Table I). However oxprenolol, which is more hydrophilic than alprenolol, gives capacity factors that are more than three times higher on the al-AGP column. The opposite retention order was obtained using a normal reversed-phase column (LiChrosorb RP-8)“. A reasonable explanation of the higher retention of oxprenolol on the al-AGP column may be that the oxygen in the allyloxy group interacts specifically with the chiral phase. Ester and acetyl derivatives. Preparation of ester derivatives of acids and acetyl derivatives of amines can be an effective way of increasing the separation factors of acids and amines, respectively. This can be illustrated by the following examples: the enantiomers of mandelic acid have been separated as ester derivatives, and the enantiomers of trans AJ 126, a primary amine (structure see Fig. l), have been separated after acetylation. The resolution of the acetylated trans AJ 126 enantiomers is shown in Fig. 5; a separation factor of 4.95 was obtained, and the peaks had capacity factors of 0.88 and 4.33. The mandelic acid enantiomers were not resolved on an al-AGP column. However, the enantiomers can be separated as methyl and ethyl esters. The chromatographic data are summarized in Table II, and a chromatogram of the separation of TABLE II CHROMATOGRAPHIC DATA FOR MANDELIC ACID AND ITS ESTERS Conditions: column, 100 x 3.0 mm I.D., 147 mg of ai-AGP per gram of solid phase; mobile phase, phosphate buffer (pH 7.0; p = 0.02) with the addition of 2% 2-propanol.
Mandelic acid Mandelic acid methyl ester Mandelic acid ethyl ester l
k’,”
a
1.13
1.00
1.04
1.27
1.47
1.93
Capacity factor of the 6rst eluted enantiomer.
I
J. HERMANSSON
-
mm 5 0 Fig. 6. Resolution of racemic mandelic acid ethyl ester. Column, as in Fig. 5; mobile phase, 2% (v/v) 2propanol in phosphate buffer @H 7.0; p = 0.02); flow-rate, 0.5 ml/mm.
the enantiomers of the ethyl ester derivative is shown in Fig. 6. Acids with pK, values between 3 and 8.5 have also been separated directly on the al-AGP column, without derivatization, with separation factors up to 5. The results will be published elsewhere4. ACKNOWLEDGEMENT
I am grateful to Mr. Christer Bergh for skillful technical assistance. REFERENCES 1 2 3 4 5 6 7 8 9 10 11
J. Hermansson, J. Chromurogr., 269 (1983) 71. J. Hermansson, J. Chromufogr., 298 (1984) 67. J. Hermansson, M. Eriksson and 0. Nyquist, J. Chromarogr., 336 (1984) 321. J. Hermansson and M. Eriksson, J. Liq. Chromatogr., (1985) in press. J. D. Adams, Jr., T. F. Woolf, A. J. Trevor, L. R. Williams and N. castagnoli, Jr., J. Phurm. Sci., 71 (1982) 658. U. Hacksell, A. M. Johansson, L. E. Arvidsson, J. L. G. Nilsson, S. Hjorth, A. Carlsson, H. Wilstrom, D. Sanches and P. Lindberg, J. Med. Chem., 27 (1984) 1003. I. W. Wainer, T. D. Doyle, Z. Hamidzadeh and M. Aldrige, J. Chromutogr., 268 (1983) 107. W. A. Kiinig, K. Ernst and J. Vessman, J. Chromatogr., 294 (1984) 423. I. W. Wainer, T. D. Doyle, K. H. Donn and J. R. Powell, J. Chromurogr., 306 (1984) 405. T. D. Doyle and I. W. Wainer, J. High Resold Chromarogr. Chromatogr. Commun., 7 (1984) 38. S. 0. Jansson, I. Andersson and B. A. Person, J. Chromutogr., 203 (1981) 93.